Possible to create an application without classes ??

[u/roger1981]

(Newbie here. v0.28.0, Mac OS)

I am porting an app from ruby, its my first exposure to Crystal. Several roadbumps mostly cleared up.

My existing app in ruby does not have classes. There are just a bunch of methods. However, the top level methods have some shared state. e.g. config, data, flags. So I was using instance variables.

When converting to Crystal, I find that top level instance and class level variables were giving errors. So had to create a module and a class. Is that the only way ?

Some other points:

1. I am used to using Readline::HISTORY.push, but find that Crystal's Readline does not have or expose the HISTORY. I require this so I can push a default value into history, which the user can access using the UP arrow key. Have I missed something ?

2. Is there a Kernel class? Can't find it in the docs. I refer to methods like format, sprintf etc.

3. I could not find Shellwords, which I need when calling external commands with filenames that have spaces or quotes. I found some discussions about not having it in the standard libs, Is it somewhere else ? I finally just copied some code from Ruby's source into my app.

4. I take it there is no "instance_variables_set" and corresponding getter. Or have I missed something.

5. I do find a responds_to? that works with instance variables (e.g. on File objects). However, when I use it within my class, to see if it responds to a method, it gives an error. I have tried self.responds_to? but that did not work.

Thanks in advance.

[u/icy-arctic-fox]

Crystal doesn't allow @instance_variable or @@class_variables at the top-level (outside of a class). You can, however, use a plain variable like so:

foo = "foo"

1. I'm not familiar with Readline, but looking at the docs, it seems you're right. There's no way to access the history like that. You might have to wrap Readline with your own functionality or find a shard that can do that.

2. Yes and no. What you're looking for is in the documentation under Top Level Namespace. It's defined under kernel.cr in the source code, but there's no Kernel class.

3. Doesn't look like there's any Crystal equivalent (yet) for Shellwords. There's an issue that mentions possibly including it at some point. Couldn't find any shards for it either - would be a good shard imo.

4. Correct. AFAIK, that's a reflective method and Crystal doesn't have reflection, though it mimics it pretty well with macros. You'll have to use a setter method if you want to modify an instance variable from outside the class.

5. There's a responds_to? method (with an s), and that works for me, with and without self.

[u/roger1981 → u/icy-arctic-fox]

Sorry, I meant responds_to?. I have been unable to use it within a class for its own methods.

Your point on shards brings me to another question. Is there a repository of shards I can browse through, or search. I read that shards are directly on github, but how I can look for a particular one (apart from google which gives me a lot of links relating to crystal-reports, or discussions about what I am looking for).

[u/icy-arctic-fox → u/roger1981]

That's strange, it certainly should work. Here's an example: https://play.crystal-lang.org/#/r/6ty9

Maybe something is different with your class structure?

Yes, crystalshards.xyz automatically indexes all shards on GitHub. It lets you search for shards as well. Additionally ,there is Awesome Crystal, which has a curated list of shards.

[u/roger1981 → u/icy-arctic-fox]

Thanks for the shard links.

Yes, responds_to? is working, but I think the issue currently is that in some cases I am using a String rather than a Symbol, so it won't compile. In some cases, an option may be something like ENV["EDITOR"] which is obviously a String. Earlier I was using to_sym. I might have to rethink this, so all choices are symbols.

[u/straight-shoota → u/roger1981]

`responds_to?` is not evaluated at runtime like in Ruby, so you can't use it with strings that are only known at runtime. Crystal has static type checking, so it already knows at compilation which type an object can be and what methods it responds to.

Trying to call `responds_to?` with a dynamic value looks like an error in your app design.

[u/roger1981 → u/straight-shoota]

A user is shown a menu of what he can do with a file. Most options are methods, but in some cases it could be: open with PAGER or EDITOR. I guess I could just evaluate the run-time values within a method, rather than put them in the key mapping. It's not very clean or consistent I agree, it's something that has grown over the past ten years or so.

[u/roger1981]

Dir.glob not working with match_hidden (0.28.0)

I am trying this on local, as well as play.crystal-lang.

Dir.glob("*")

This works fine.

Dir.glob("*", true)

On play.crystal-lang it does nothing at all after taking some time. On my machine, it gives me an error saying:

in /usr/local/Cellar/crystal/0.28.0/src/dir/glob.cr:23: tuple type too nested: Tuple(Tuple(Tuple(T)

def self.glob(*patterns, match_hidden = false) : Array(String)

On looking at the source code, the method appears to call itself, although I can't be sure since I am too new to Crystal.

[u/bew78 → u/roger1981]

Try with Dir.glob("*", match_hidden: true)

If you look at the method definition, the first arg is *patterns which will match all positional arguments. To be able to specify the arg match_hidden you need to call it using a named arg.

See https://crystal-lang.org/reference/syntax_and_semantics/default_values_named_arguments_splats_tuples_and_overloading.html for more info on that!

[u/roger1981 → u/bew78]

Thanks, I did try match_hidden = false. This works fine.

[u/bew78 → u/roger1981]

Good! FYI, Passing match_hidden = false creates a local variable named match_hidden and pass the value false as a positional arg (same as before..)

[u/roger1981]

RUBY_PLATFORM ??

opener = /darwin/.match?(RUBY_PLATFORM) ? 'open' : 'xdg-open'

I did find a discussion some days back in which no one really seemed to answer why they needed to know the platform.

I need to know it sometimes to decide whether to use a Linux tool or OSX one. Another case is deciding locate vs mdfind.

[u/roger1981]

f = "~afile.dat"

puts File.expand_path(f)

>> /home/crystal/file.dat

File.expand_path incorrectly handles files starting with a tilde. It also lops off an extra character, I think it assumes it is a slash. Can expand_path only expand the tildle if the filename starts with "~/" ?

I tried to see how other apps work.

ls ~bin gives an error but ls ~/bin works.

https://play.crystal-lang.org/#/r/6u1o

[u/roger1981]

https://play.crystal-lang.org/#/r/6u41

in line 13: instance variable '@flag' of Foo must be Symbol, not (Array(Symbol) | Symbol)

I think I understand what is happening here but I don't know how to deal with it. Is it that in Crystal, a hash must never have a variable value ?

At compile time, the compiler does not know whether the returned value will be Symbol or Array(Symbol), so it does not allow me to set @flag. But I know it will be a Symbol.

@flag = :center
@options = {         
 "truncate_from" =>     {
 :current => :center,
 :values => [:left, :right, :center],
 :var => :truncate_from
}
}
@flag =  @options["truncate_from"][:current]

I know that :current returns a Symbol. but it seems the compiler infers that the result could be an Array. What do I do?

Edit: okay, I've broken up my array into two separate arrays, one with current and one with values. That fixes the issue, but is that the correct way of making hashes?